I believe what he meant was, 'How do I make a sprite stay a certain distance from the player in the angle he's facing'
The way its worded could easily be mistaken for, 'How do I make one sprite always appear on top of another'
However in this case I would also recommend putting it in a UI layer above the game layer anyway so, for example, the aiming reticle doesn't get hidden by some wall you added later.